This invention is directed toward bicycle brakes, and more particularly toward a mechanism for adjusting the return force on a lever arm of a caliper disc brake.
Disc brakes are being included on more and more bicycles as consumers are ever increasingly demonstrating a preference for disc brakes over conventional rim brakes such as caliper brakes, cantilever brakes and side pull cantilever brakes. Mechanical disc brakes and ball bearing mechanical disc brakes are gaining in popularity and consumer preference as their ability to provide powerful, reliable and smooth actuation are approaching, and in some cases exceeding, that of hydraulic disc brakes.
One common feature of mechanical disc brakes is the inclusion of a spring for applying a return force to a lever arm which actuates a caliper brake mechanism. The return spring must apply a force sufficient to return the lever arm to an unactuated position but must not apply such a strong return force that it is difficult for a user to actuate the brakes. Because users may have different physical strength and different preferences in the feel of the brakes it is highly desirable to allow users to adjust the amount of return force to meet the users needs and preferences. In addition, as the bike is used, it is not unusual for debris or corrosion to accumulate within the cable or lever which actuates the pivot arm, which can require an increase in the amount of return force applied to the pivot arm. For this reason as well, it is useful and desirable to be able to adjust the amount of return force applied to the caliper brake lever arm.
One conventional form of the return spring is a coil spring having axially extending ends. One known structure for adjusting the force of the return spring is providing radially spaced holes about the return spring axis in the lever arm for receiving one of the axially extended ends of the coil spring. The return force can be varied by choosing one of the limited number of holes.
A significant problem with this structure is it requires disassembly of the caliper in order to adjust the return spring force. Thus, if a user is on a ride and needs to increase the return force on the lever arm due to build up of debris in the cables or elsewhere in the system, it is extremely time consuming and difficult to do, requiring numerous tools the user may not have on hand. In addition, the user has only a limited choice of return forces which may not meet the desire of the user.
The present invention is directed toward overcoming one or more of the problems discussed above.
A bicycle disc brake caliper includes a lever arm rotatable about a pivot axis in an advancement and a return direction. A rotary to linear linkage between the lever arm and a brake pad translates rotation of the lever arm in the advancement and return directions to linear advancement and return, respectively of the brake pad. A spring is coiled about a spring axis parallel to the pivot axis. The spring has a first end fixed against rotation relative to the lever arm and a second end rotatable with the lever arm about a spring axis. The spring applies return force in the return direction to bias the lever in the return direction. A screw which is selectively rotatable about a screw axis is operatively associated with one of the first and second ends of the spring to selectively rotate the spring end relative to the other end about the spring axis by rotation of the screw about the screw axis. The screw ends can be moved relative one another independent of movement of the lever arm to adjust the return force applied by the spring to the lever arm. In a preferred embodiment, a spring tension biasing plate is rotatable about the spring axis. The movable end of the first and second ends is attached to the spring biasing plate for movement with the spring biasing plate. The screw engages the spring tension biasing plate along the screw axis to rotate the spring tension biasing plate about the spring axis which thereby adjusts the return force applied by the spring to the lever arm. The screw may threadably engage one of the lever arm and the caliper housing fixed against rotation. Alternatively, the spring tension plate may include an internally threaded bore radially spaced from and transverse the spring axis with the screw being threadably received in the internally threaded bore and the screw axially abutting a stop on the lever arm. A structure is preferably provided for limiting rotation of the first and second ends of the spring relative to one another.
Another aspect of the present invention is a method for adjusting the return force in a return coil spring of a bicycle disc brake caliper. The caliper has a lever arm rotatable about a pivot axis in an advancement in a return direction. A rotary to linear linkage between the lever arm and a brake pad translates rotation of the lever arm in the advancement and return directions to linear advancement and return, respectively, of the brake pad. The return spring has a spring axis and biases the lever arm in the return direction. The method includes fixing a first end of the coil spring for rotation with the lever arm and fixing a second end of the coil spring to be stationary relative to the lever arm during rotation of the lever arm. One of the first and second ends of the spring is rotated relative to the other a select infinitely variable amount within a fixed range independent of rotation of the lever arm about a spring axis to adjust the spring force applied by the spring to the lever. The ends are then secured relative to one another with the ends relatively rotated the select amount. The steps of rotating the first and second ends and securing the first and second ends which have been rotated the select amount may be performed by providing a screw operatively associated with one of the first and second ends along an axis of the screw and rotating the screw about the screw axis a select amount.
The apparatus and method of the present invention provides a mechanism for adjusting a return force applied to a caliper brake lever arm that is accessible outside the caliper housing. Thus, no disassembly is required to vary the return force which can allow debris to enter the housing and which is extremely inconvenient for a user. In addition, the method and apparatus allows for infinite adjustment of the return force within a defined range to meet the needs and desires of the user. The return force can be adjusted simply and easily with a single tool. The mechanism is provided with a small number of easily machined parts and can therefore be provided at minimal cost and with minimal increase in the complexity of assembly of the caliper disc brake.